Plastic parts can be assembled by placing a part with clearance holes over a mating part with protrusions (bosses) that extend through and above the holes to provide a volume of plastic that can be reformed (staked) into a rivet type connection that secures the two parts. Staking is accomplished using a variety of methods.
One staking method includes an ultrasonic method that brings a punch into contact with a boss. The punch is then vibrated (e.g., vertically) at a high frequency to excite the plastic molecules and generate enough heat to soften/melt the plastic to form a rivet. A hot air, cold punch method blows heat onto a boss to heat it to a temperature that allows forming. A punch is then extended to form the heated boss into a rivet. Infrared staking directs infrared energy to a boss until the boss has absorbed a prescribed amount of energy. At that time, a punch is extended to form the boss into a rivet. Impulse staking pulses electric current through a resistive (tip) punch to heat the punch to a temperature sufficient to melt a boss. In a hot punch method, a punch is heated to heat a plastic boss to a molten state. Heat and pressure reform the plastic into the shape of the punch face to form a rivet clamping two pieces together. There are various methods used to heat the punch including conduction (e.g., a coil heater) and induction (e.g., electrical impulse).